Proteins are often employed to encapsulate a component so that it can be released over a period of time. For example, an article entitled “Encapsulation of Essential Oils in Zein Nanospherical Particles” (Parris, et al., J. Agric. Food Chem. 2005, 53, 4788-4792) broadly describes the encapsulation of thymol in zein nanospheres by mixing the oil with zein particles in the presence of a solvent (e.g., ethanol). The particles are said to be useful for oral or injectable administration of biological materials into the body. Another article entitled “Controlled Release of Thymol from Zein Based Film” (Mastromatteo, et al., J. Innovative Food and Emerging Technologies 2009, 10, 222-227) broadly describes films formed by dissolving corn zein and glycerol into ethanol, and thereafter adding thymol to form a solution. The solution is poured into a Petri dish and dried to form the film.
One problem with the techniques described above is that they generally rely on solvents (e.g., ethanol) to help dissolve the oil into a solution. A disadvantage of the use of solvents is that both the oil and protein must be soluble in a common solvent system, which puts a limit on what type of components may be employed in the composition. Also, solvent-based solutions require a substantial amount of time, energy, and material for processing. Still further, a portion of the oil may escape from the solution when the solvent is evaporated, which requires the use of a greater amount of the oil than would normally be needed. Notwithstanding the above, the ability to use a “solventless” process is complicated by the tendency of proteins to lose their flow properties when exposed to the intense shear and elevated temperature normally associated with melt processing. For example, proteins may undergo a conformational change (“denaturation”) that causes disulfide bonds in the polypeptide to dissociate into sulfhydryl groups or thiyl radicals. Sulfhydryl groups form when disulfide bonds are chemically reduced while mechanical scission of disulfide bonds causes thiyl radicals to form. Once dissociated, however, free sulfhydryl groups randomly re-associate with other sulfhydryl groups to form new disulfide bond between polypeptides. Thiyl radicals can also randomly re-associate with other thiyl radicals forming new disulfide bonds or thiyl radicals can react with other amino acid functionality creating new forms of cross-linking between polypeptides. Because one polypeptide contains multiple thiol groups, random cross-linking between polypeptide leads to formation of an “aggregated” polypeptide network, which is relatively brittle and leads to a loss of flow properties.
As such, a need currently exists for a protein composition that can be readily melt extruded.